1. Field of the Invention
This invention relates to the process of fabricating thin film multi-layer magnetoresistive sensors. More specifically, the invention relates to a process for reducing damage to magnetic tunnel junction (MJT) sensors during the formation of the air bearing surface.
2. Description of the Related Art
FIG. 1 (Prior Art) is a partial cross sectional view of a thin film read/write head combination. A read head 104 employing multiplayer thin film magnetoresistive (MR) sensor 106 is combined with an inductive write head 102 to form a combined magnetic head 100. In a magnetic disk or tape drive an air bearing surface (ABS) of the combined magnetic head is supported adjacent to the moving magnetic media to write information on or read information from a surface of the media. In a write mode, information is written to the surface by magnetic fields that fringe across gap 114 between upper pole piece 112 and lower pole 116 piece of the write head 102. Write head 102 also comprises yoke 120, coil 118, backgap 122, insulation layers 124, lower pole layer 126, and insulation layer 128. MR sensor 106 is situated between two shield layers 108 and 110 and an oxide layer 109. In a read mode, the resistance of MR sensor 106 changes proportionally to the magnitudes of the magnetic fields from the moving magnetic media. When a sense current is conducted through MR sensor 106, resistance changes cause potential changes that are detected and processed as playback signals.
The MR sensor may be any one of a plurality of MR-type sensors, including anisotropic magnetoresistive (AMR), giant magnetoresistive (GMR), magnetic tunnel junction (MTJ) or tunneling giant magnetoresistive (TMR), spin valve, spin tunneling, and current perpendicular to plane (CPP) sensors. MTJ sensors typically employ a multi-layered structure which includes a tunnel barrier layer positioned between two groups of ferromagnetic layers. The entire multi-layer structure is often referred to as a “stack”. The tunnel barrier is a very thin dielectric layer, composed of a material such as aluminum oxide, while the two groups ferromagnetic layers are typically formed of a plurality of electrically conductive ferromagnetic materials and layers. On one side of the tunnel barrier, the magnetization direction of the ferromagnetic layers is “pinned” and provides a reference direction for the MTJ head. However, the magnetization direction of the ferromagnetic layers formed on the other side of the tunnel barrier rotates freely in response to an external magnetic field from the magnetic medium proximate to the ABS. As the magnetization of the freely rotating ferromagnetic layer rotates in response to the external magnetic field from the magnetic medium, the resistance of the tunnel barrier changes, which can be measured as a change in resistance of the MTJ sensor.
FIG. 2 (Prior Art) is a schematic block diagram 200 of a simplified process for making a MTJ sensor. This process is not limited to the MTJ sensors, but applies to other types of multi-layer MR sensors as well. In step 202, the multi-layer stack 106 is formed on shield layer 108. This is followed by deposition of oxide layer 109 and shield layer 110, and the remaining write head structure above shield 110. In step 204, the structure is mechanically lapped perpendicular to layers 108-110 (and the layers in the MJT sensor) to initiate formation of the ABS. The term initiate is used to denote that the actual ABS is formed in a subsequent ion milling step 206, which removes typically 5 to 10 nm of mechanical damage (smearing and debris) at the lapping surface. The layer of smearing and debris is detrimental to the sensitivity of the MJT sensor because the layer forms a low resistance path across the insulating tunnel barrier. However, the ion milling process can also introduce damage into the structure of the MJT sensor.
What is needed is a process for forming the ABS of a multi-layer MR sensor that avoids the damage produced by mechanical lapping and the subsequent ion milling of the prior art.
United States Patent Application Publication 2004/0262258 discloses a method of forming a tunneling magnetoresistive head which begins by forming a tunneling magnetoresistive stack having a tunnel barrier. An air bearing surface is formed of the tunneling magnetoresistive stack. The air bearing surface is ion etched causing a deficiency of a constituent in a portion of the tunnel barrier adjacent the air bearing surface. The deficiency of the constituent is replenished in the portion of the tunnel barrier adjacent the air bearing surface to restore the electrical properties of the tunnel barrier.
United States Patent Application Publication 2003/0179497 discloses a magnetic head having improved overwrite capabilities and reduced fringing fields along with methods of making the same. The magnetic head has a first pole piece and a second pole piece. The first pole piece includes a first bottom pole piece layer, a pedestal portion formed over the first bottom pole piece layer, and a notched top pole portion formed over the pedestal portion. A gap layer separates the second pole piece from the notched top pole portion. The pedestal portion has a first saturation magnetization M.sub.S1 and the top pole portion has a second saturation magnetization M.sub.S2 that is greater than the first saturation magnetization M.sub.S1. The top pole portion has a substantially planar top surface over which a portion of the gap layer and the second pole piece are formed.
United States Patent Application Publication 2003/0168627 discloses a slurry for chemical mechanical polishing (CMP) of a refractory metal based barrier film which includes a plurality of composite particles and at least one selective adsorption additive, such as a surfactant or a polymer. The composite particles have an inorganic core surrounded by the selective adsorption additive. The refractory metal based barrier film does not substantially adsorb the selective adsorption additive surfactant, while other exposed films substantially adsorb the surfactant. A method for chemical mechanical polishing (CMP) a refractory metal based barrier film includes the steps of providing a slurry including a plurality of composite particles and at least one selective adsorption additive. The invention can be used for a single step CMP process for polishing a structure including a gate or interconnect metal layer, a refractory metal based barrier film and a dielectric film, first removing gate or interconnect overburden metal and then removing the overburden regions of the refractory metal based barrier film in a single polishing step.
U.S. Pat. No. 6,696,226 discloses a method of making a magnetic read/write head using a single lithographic step to define both a write coil and a pole tip structure. The use of a thin image resist layer over a hard reactive-ion etch mask and image transfer techniques allows very high resolution optical lithography which can accommodate formation of a very compact coil and pole structure. The use of a single high resolution lithography step on a planarized structure to define both a write pole tip and a write coil coplanar with the write pole tip avoids the problems of reflective notching associated with lithography to define the pole tip in the vicinity of non-planar features of the coil structure and also eliminates alignment inaccuracies inherent in separate lithography processes for the coil and pole.
U.S. Pat. No. 6,859,998 discloses an article formed as a substrate having a projection extending outwardly therefrom. The article may be a magnetic recording head and the projection a write pole. The projection has a width in a thinnest dimension measured parallel to a substrate surface of no more than about 0.3 micrometers and a height measured perpendicular to the substrate of not less than about 5 times the width. The article is fabricated by forming an overlying structure on the substrate with an edge thereon, depositing a replication layer lying on the edge, depositing a filler onto the edge and the substrate, so that the filler, the replication layer, and the overlying structure in combination comprise a continuous layer on the substrate, selectively removing at least a portion of the replication layer from a free surface of the continuous layer inwardly toward the substrate, to form a defined cavity, and depositing a projection material into the defined cavity to form the projection.